This invention relates to a gasket for socket-spigot connections having a relatively wide sealing gap and relatively large work tolerance for the nominal width of the width of the sealing gap, in other words, for relatively large tolerances for the inner diameter of the socket and the outer diameter of the spigot end which must be sealed against each other when the socket-spigot connection is formed.
Such conditions occur particularly for socket connections of pipes made from mineral materials and having large nominal diameters.
Such mineral materials which have large tolerances are particularly fired or vitrified clay and concrete. Larger tolerances also result when manufacturing pipes made out of other mineral materials, for example, pipes consisting of fiber reinforced concrete and particularly asbestos cement.
For all such socket-spigot connections of pipes consisting of mineral materials, the problem of sealing the socket-spigot connection increases when the nominal diameter of the pipes increases. That is caused on one hand by the increasingly larger nominal breadths of the sealing gap, in other words, by the increasingly larger distance between the inner wall of the socket and the outer wall of the spigot end. Simultaneously, the absolute values of the tolerances of the sealing gaps increase, these tolerances resulting from the process of manufacture. The other cause is the increasing weight of the pipes which cause, independent of external additional loads, a considerable shear stress of the socket-spigot connection and thus a considerable strain vertical to the longitudinal axis of the pipes. When pipes are laid horizontally, for instance, the full weight of the spigot end lies at its lower area upon the lower area of the socket, thereby leading to high pressures, for example, on the rubber and elastic gasket in this area. In the oppositely disposed region of the socket connection, the deformation due to pressure and/or tension of the elastic-rubbery gasket is considerably reduced by the significant enlargement of the sealing gap. This leads to a noticeable reduction of the inner and outer pressure up to which the whole socket-spigot connection may be called an effective one. This reduction of the limiting pressure of tightness of the socket-spigot connection amounts in conventional gaskets, which may be used successfully with pipes with small nominal values, generally up to 100%. The sometimes effective and today generally used socket-spigot connections gasketted with rubber rings for small nominal diameters of pipes were not capable of being used for large nominal diameters of pipes due to the aforementioned problems. On the one hand, the profiles of the sealing rings must be so large due to the large standard breadths of the sealing gaps, that they would become extremely expensive for practical use due to the large amount of raw materials used. On the other hand, the known profiles of sealing rings, which were effective for small nominal values, would not be able to bridge manufacturing tolerance breadths of the sealing gap. When the profiles are dimensioned too generously, too large push-in forces are needed for the pushing in of the spigot end at the lower end of the tolerance range. These push-in forces are so high that they frequently cannot be exerted in fact, while too small dimensioned sealing rings are not capable to assure crown tightness of the socket connection even at low shear stresses. A profile of a sealing ring which satisfies the demands in both limiting ranges, in other words, for the smallest and for the largest sealing gap, demanded by the tolerances, is heretofore not known.
Many attempts have heretofore been published in order to solve the problems occurring particularly with socket-spigot connections of pipes made out of mineral materials and having larger nominal diameters. All attempts for practical use in this field seek to use instead of a single elastic sealing ring, a combination of inner and outer annular lip seals which are supported and stabilized by embedded or interdisposed jacket-shaped braces.
The most useful of such prior art devices is disclosed in Federal Republic of Germany DE No. 27 26 959 A1. Instead of a single elastomeric sealing ring, two such sealing rings are provided, one of them sealing at the inner wall of the socket, the other sealing the outer wall of the spigot end. The sealing rings are integrally connected to a sealing insert, substantially looking like a cylinder jacket by means of relatively thin and extendable ring bars, and the sealing insert also is relatively thin. This sealing insert also has a relatively thin reinforcement which resists bending. The sealing insert also has diminutions of the outer diameter into which the material of the sealing rings may press where the planes to be sealed are at radially narrow and most narrow distances.
A disadvantage of all embodiments of the basic idea in this prior art publication is that the whole breadth of the sealing gap and the whole tolerance of the sealing gap breadth must be substantially intercepted by the elasticity of the rubber. This known gasket is thus capable of solving the problem of material economisation but is not capable of solving substantially the problem of reducing the push-in force into the most narrow sealing gaps, while simultaneously assuring a high degree of pressure-resisting tightness at great shear stresses in the range of large and largest breadths of sealing gaps resulting from the manufacturing tolerances.
Considering this state of the art, an object of the present invention is to provide a gasket for a socket-spigot connection of the aforementioned type which is capable of improving the shearing resistance with a minimal use of material for the elastomeric sealing rings, particularly for socket-spigot connections between heavy pipes with large diameters, relatively broad sealing gaps and relatively large manufacturing tolerance for the breadth of the sealing gap, and which is capable of lowering the push-in forces needed for the spigot end to produce a pipe plug connection in the range of a sealing gap which might be narrow or extremely narrow as the tolerances dictate.
This objective is achieved by providing a gasket according to the invention for a socket-spigot connection consisting of a substantially cylindrical ring as a sealing insert, carrying on its outer wall at least one sealing ring sealing against the inner wall of the socket and carrying on its inner wall also at least one sealing ring sealing against the outer wall of the spigot end. The sealing insert is made out of a material which is stable in its shape and has a radial wall thickness equal to or slightly smaller than the smallest breadth of the sealing gap allowed by the manufacturing tolerance. "Slightly smaller" and "slightly larger" also relating to diameters means only negligible oversize or undersize of the noted size, which still permits free mutual sliding past of the respective parts, thus just the practically friction-free application of the sealing insert into the socket. This assures the practically friction-free setting of the spigot end into the sealing insert when the socket has the smallest inner diameter within the tolerance range and when the spigot end has the largest outer diameter within the tolerance range.
Annular grooves are provided on the sealing insert for accepting the sealing rings, the volume and profile of such grooves being so dimensioned that they are capable of containing completely an apportioned sealing ring and the sealing ring does not surpass a predetermined limiting value for tension deformation and material compression when it is completely pressed into the annular grooves.
Mainly when using lip rings, particularly spreading lip rings, the push-in forces may be kept extremely small even in a most narrow sealing gap, dictated by the tolerances, when the annular grooves in the sealing insert are shaped as aforedescribed. The broad radial dimensions of the sealing insert in relation to the sealing gap enables this form of stable sealing insert to immovably accept the whole shearing forces like a buffer already after a relatively short radial displacement of the spigot end relative to the socket or, in reverse, of the socket relative to the spigot end. Thus there is no need anymore to absorb occurring shear stresses by elastomeric means. In other words, the sealing rings may be built right away for much smaller deformation of material because the sealing rings do not have to intercept the shearing forces. Thus the sealing rings used for the invention may now make much more use of liptensions in order to exert the needed sealing pressure. A lowering of the needed minimum material distortion in favor of a larger share of lip tension in the sealing ring results not only in a greater saving of material, but reduces additionally and simultaneously the push-in forces needed in the region of the narrowest sealing gap. Sealing rings much thinner than in known gaskets may be used because the elastic sealing rings fulfill now only the sealing function and not the carrying of the load because the shearing forces are borne by the sealing insert itself.
The annular grooves provided in the inner wall and the outer wall of the sealing insert have preferably a generally flat V-shaped profile and serve to accept the sealing rings which have V-shaped profiles looking in the same direction. The included angle of the profile of the sealing rings is smaller than the included angle of the annular groove profile. The included angle of the profile of the sealing rings lies preferably in the area of approximately 90.degree..
The sealing ring may be fastened to the bottom of the sealing groove by aid of its base area, in other words the area radially opposed to the area enclosed by the V-shaped lips. It may, for example, be glued on, be an integral part, or may be clamped on by clamping means or may be shaped like a circular bead in the base area and may abut in a T-slot which has a complementary profile and is located in the bottom of the groove. The base area of such a spreading lip-ring may also have a rectangular, square or any other cross section and may be laid, glued or clamped into a T-slot in the base of the groove having a complementary profile. When the base area of the sealing ring has a circular bead shape and when the annular groove has a circular profile, an articulating effect results between the sealing ring disposed in this annular groove and the sealing insert. This articulating effect allows swivelling of the sealing ring in an optimal position. In such a case the annular T-slot in the base of the flat V-shaped annular groove is preferably slightly and axially one-sided undercut. It is undercut in the radially inside lying annular groove of the sealing insert at the side looking towards the socket base and in the radially outside lying annular groove of the sealing insert at the side looking towards the socket opening. The result of this construction is that the articulatingly disposed spreading lip sealing rings are fixed against any axial displacement when the sealing insert is put into the socket or when the spigot end is pushed into the sealing insert, respectively.
Additional stabilization of the gasket may be obtained by integrally forming an annular inner flange at the front side of the sealing insert considered looking towards the socket base. The free inner diameter of that flange is distinctly smaller than the smallest outer diameter of the spigot end (within the range of the manufacturing tolerance) and slightly larger than or at least as large as the largest inner diameter (within the range of the manufacturing tolerance) of the spigot end of the socket-spigot connection to be prepared according to the specifications. This relationship assures that the frontal side of the spigot-end sits within its whole tolerance range upon the annular plane of the inner flange of the sealing insert which faces towards the socket opening and that the sealing insert is thereby stabilized and fixed.
According to one embodiment of the invention, the sealing insert has preferably a complete axial length at least substantially equal to the depth of the groove, in other words equal to the distance between the rim of the socket opening and the socket base. Due to the fact that these axial dimensions are frequently not very large and the V-shaped ring grooves require axially relatively large spaces, the ring grooves are preferably disposed in the sealing insert in such a manner that adjacent or neighboring legs, respectively, of each individual either radially inwardly open or radially outwardly open ring groove overlaps to a large extent or completely in a radial projection. The degree of overlap must be evident so that enough material remains in the area of the dividing walls so that the stability of the sealing insert is assured.
The sealing insert itself may consist in principle of any form of stable material, for instance metal, ceramic, plastic or reinforced plastic. The sealing insert consists preferably of such materials which may be manufactured at low price and with relatively good precision. The sealing insert consists preferably of a plastic, a mainly fiber-reinforced plastic or of relatively hard compounded elastomers. When the sealing insert consists of elastomers, the softer compounded sealing rings are preferably integral parts of the sealing insert or they are molded on.
When the sealing insert has an inner flange, resting upon the socket base, this inner flange may have, for improved tightening, additional sealing parts working frontally on one or both of its surfaces. They may be, for instance, molded-on sealing beads, interposed O-rings or molded-on annular lips.
Other features which are considered characteristic of the invention are set forth in the appended claims.
Although the invention is illustrated and described in relationship to specific embodiments, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.